HMOX1 and acute respiratory distress syndrome: Moreover, treatment with HO-1 inhibitors such as zinc protoporphyrin IX (ZnPPIX) or tin protoporphyrin IX (SnPPIX) led to an enhancement of ALI/ARDS signals in the case of sepsis but had no effect in the cases of hyperoxia and experimental cerebral malaria [16, 24, 32].